1. Field of the Invention
The present invention relates to devices and methods for cooling, and more particularly, the present invention relates to a device and method for cooling substances using electric fields.
2. Background of the Invention
Thermoelectric methods for cooling (such as Peltier coolers) prove inefficient. Standard methods used in refrigeration and air conditioning systems are based on vapor compression of Freon gases or chlorofluorocarbons and hydrochlorofluorocarbons. These refrigerants pose serious risks to public health and the environment. These systems are also bulky and therefore cumbersome.
As electronics become more sophisticated, alternative methods for cooling will be required. For example, as transistor densities increase, processors consume more power and generate more heat.
Research continues for substances which can undergo large thermal changes as a response to external stimuli. Research is also ongoing to develop devices and methods for utilizing such stimuli as electric fields, to generate cooled substances more efficiently than state of the art systems.
Cooling methods and prototypes driven by electric fields and based on solid-state refrigerants operate on the electrocaloric effect (ECE). The ECE is a phenomenon in which a material shows a reversible temperature change under an applied electric field. The ECE is the result of entropy variations with polarization, e.g., isothermal polarization of a ferroelectric reduces its entropy while depolarization increases it. Thermal changes are largest in these solid ferroelectric materials near their polar-to-non-polar change points. The application of an electric field induces a polarization in a ferroelectric, which in turn heats it up because of the laws of thermodynamics. But no physical phase change occurs in these systems inasmuch as they operate near the solid-to-solid phase transformation temperatures of the ferroelectric. In summary of this point, solely solid state materials are acted upon by electric fields and remain as solids.
But these systems have drawbacks. Ferroelectrics, which are materials that exhibit spontaneous reversible polarization, exhibit caloric effects that are only a few milliKelvin per kV/cm, with the effect limited by their breakdown voltages. The effect can be enhanced somewhat by using ferroelectric thin films, however, these still have inadequate cooling power. Chip scale electrocaloric oscillatory refrigeration devices using solid state regenerators display a 6 K temperature span at near room temperatures (e.g. 10° C. to 40° C.). Specifically, the latent heats of solid-solid transformation in ferroelectrics is about 0.1 to 42 kJ/kg.
Magnetically cooled systems require large magnetic fields to be useful. Such fields are hard to generate and sustain. Also, the required magnets comprise expensive rare earth elements.
A need exists in the art for a device and method for efficiently cooling substances in room temperature environs when subjected to external stimuli. The substance should be environmentally friendly in that it should not be toxic to users, the ozone layer, or fauna. The system and method should impart large temperature changes and therefore high cooling power. The system and method should be safe and relatively inexpensive.